Page 132. This page is in the page-by-page raw-dumps section.

I list the output-control macros here.

  • 2.1. sequential-enabling output

    Faulty implementation. Unlike what an example figure suggests, it does not provide a sequential order of execution. The full-reversal of execution order is possible. (This may be because of the false assumption stated in the copycat82 that, a macro would "start execution as soon as enabled." But that cannot be true, as long as those macros are built-up from the regular Petri net transitions, which may wait as long as they may, and also may altogether choose not to fire.

  • 2.2. and-output

    Corresponds to the F(ork)-transition of E-nets. It is, of course, the regular Petri net transition that has two output places.

  • 2.3. xor-output

    Corresponds to the X-transition of E-nets (but nondeterministic, data being discarded), and to the OR-output-lgic of SARA (UCLA graphs).

  • 2.4. or-output

    Is different from X-transition in that, it may also result in both of the output places being enabled. (this is also nondeterministic, data being discarded).

Fig.5.4 The Output transfer macros as implemented in Petri nets

And even worse, in several cases, even among the most trivial, there are errors. For example, the "sequentially enabling" output macro's implementation lets even the total reversal of the execution order "in a sequence."

The output macro ';' for "sequentially enabling" Its implementation has an extra intermediate place. This leads to a potential of reversing the execution order. That is, the second enabled one may get used before the first enabled. A needless introduction of indeterminism. The confusion appears to be apparent, when we compare a figure which is supposed to be presenting a usage-example for this macro. It claims that "s1;s2;s3" would correspond to a strict sequential execution. In that example figure, the equivalent figure drawn is the ordinary Petri net way of three transitions following each other. The example is like the result we would more readily expect from the semantics in the common programming languages Pascal, C, etc. But actually, with the implementation of the macro, any order of execution is possible. It is fully nondeterministic.

Notice that, once q1 is enabled, and then also q2 is enabled, with no other requirement, then q2 may actually be used before q1. Nothing, within Petri nets semantics, would suggest otherwise. The ';' macro implementation is in fig 5.4 on p.132. (In the UnPaper, it is in fig.10, on p.744, with all the same implementation.) The example is in fig 3.8.a, on p.59.

(The ordinary Petri nets transitions would suffice for the expected sequencing).

Indeed, given that the or-out and xor-out operators themselves are nondeterministic in the results, a claim could be that this is also "meant to be indeterministic" (although the specification on p.51 suggests no indterminism). But the fragility of the asrgument is that, if the as-soon-as enabled firing could be provided by the system, it would not be deterministic. It is because of that not being available, that this indeterminism is introduced. Hence, that introductiion of verbosity is just not explainable designwise. And this turns out to be a just another example of listening (and evaluating) to that Mr.Unbelievable-Ph.D. He always speaks at the borders of true versus false. Even objecting is risky because a make-do answer may be given. Yet, in the class, when the other (unlearned) students asked questions, that could bring out the errors (when he did not silence them, and suggested them to think by themselves even when they were right). Here is another fellow witness of mine, right there in his PhD thesis..

Compare Y-transition versus xor-input. Xor-input macro is one of those (as we discussed) faulty/useless four input-macros that have been derived from the Y-transition of E-nets. And xor-input is specifically chosen in its place in a figure corresponding to the fig.1 of the N&N paper.

The suggested method cannot handle the changes made to the ordinary Petri nets. As a result, it becomes very much error-prone, both for humans, as well as for machines. The changes beyond the source papers have not been handled to make things work. Once modified as such, the system becomes useless. Even the basic advantages of the ordinary Petri nets are lost. And this, essentially, totally disqualifies the UnPhD as a PhD recipient.

At the least, this leads to pushing the Petri net verification system to verify a fully explosive sort of branching. Especially, consider the behavior of the two branching-at-output macros, inclusive-OR (with behavior "any subset may happen") and exclusive-OR (with behavior "either one of the cases may be chosen"). The verification system has no possibility of pruning any branches even though the data could help a lot. That leads to larger graphs at any given level. The data and predicates, in cases of N&N and V&D, can reduce possibilities.

Further Reading

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Written by: Ahmed Ferzan/Ferzen R Midyat-Zila (or, Earth)
Copyright (c) 2004, 2009 Ferzan Midyat. All rights reserved.